Useful Information about Glacial Deposits
This trip will take us through some of the very classical glacial features of North America. We will be traveling between the Lake Michigan Lobe and the Green Bay Lobe of the Wisconsinan Glaciation. We will see examples of ice contact deposits and glacial fluvial deposits. Almost all the topography of this part of the state can be attributed to glaciation. The most spectacular feature is the interlobate moraine.
The most common features are classified as either Ice Contact or Glacial-Fluvial. The glacial-fluvial or outwash deposits are economic importance because they are major sources of sand and gravel. These deposits come in many shapes and as a result have many names based on their geomorphic characteristics.
Kames and Eskers are examples of glacial-fluvial deposits. Kames have a large number of descriptive names such as Terrace Kames, Moulin Kames, and Delta Kames. In all cases they are the result of water flowing at the margins of the glacial ice, on the ice, through the ice and under the ice. Flowing water in any environment sorts sediments based on water velocity and water volume. These glacial fluvial deposits are therefore large deposits of water-sorted sediments. In some cases they are hundreds of feet thick and acres in size. To some researchers it is important to distinguish these different forms, but for most of us it is only important to know they are water born sediments associated with the margins of the ice. Two very distinct forms are Moulin Kames and Eskers. Moulin Kames are cone shaped features caused when water swirls through the ice and leaves the sediments behind. Eskers are snake like ridges formed under the ice or on the ice as river deposits. Most of the other glacial-fluvial deposits are nondescript piles of sand and gravel.
The most common Ice contact features are Moraines. These are the result of material falling on the glaciers, or being pushed or bulldozed by the ice. We will see the Interlobate Moraine where the Lake Michigan Lobe met the Green Bay lobe of the advancing ice. Generally moraines are non-stratified deposits. Frequently they are piles of gravel, boulders, and clay all mixed together. The interlobate moraine is also the location of many kettles or kettle lakes. The kettles are formed when blocks of glacial ice are buried in the sediments on the margins of the ice. They melt over a very long time and leave behind holes in the landscape that may or may not fill with water. Minnesota is known as " the land of 10,000 Lakes " lakes that are basically kettle lakes. Northern Wisconsin also has many such lakes.
Drumlins are also on our tour. They are recognized by their elongated, cigar or canoe shape. They are elongated in the direction of the ice flow with a steep side on the up ice side. They are usually found some distance from the terminal margins of the ice (20-40 miles). Their method of formation is somewhat problematic, because one theory does not fit all drumlins. Some have rock centers or cores, and are probably just remnant bedrock highs smoothed by the glaciers. Others drumlins have stratified sand and gravel at the core, but are covered by glacial till. This type may be formed by a readvancing ice sheet that reshaped a previous deposit, such as a kame. Some drumlins have only glacial till inside of them that may be related to pressure differences at the base of the ice. In any case they are plentiful between Milwaukee and Madison WI, and Rochester and Syracuse NY.